Farmasetika Dasar:

Dosis dan Obat Tak

Tercampurkan (OTT)

Tim Farmasetika Dasar

Fakultas Farmasi

UNPAD

2012

Tujuan Pembelajaran

Mahasiswa/i mampu:

1. Mengerti definisi dosis dan interaksi

obat/OTT

2. Menjelaskan jenis-jenis dosis

3. Memahami dosis pada kondisi tertentu

4. Menghitung dosis berdasarkan rumusnya

Dosis/Takaran •Ukuran/konsentrasi obat yang diharapkan dapat

mempunyai efek kerja/daya terapi pada orang dewasa

•Jumlah yang pasti dari suatu obat yang digunakan pada

satu kali kesempatan

Macam-macam Dosis • Dosis lazim/usual dose

• Dosis maksimal (TM)

• Dosis toksik

• Dosis letalis, LD50

• Dosis kuratif

• Dosis kombinasi (TM Berganda)

Faktor Penentuan Dosis

1. Umur

2. Berat Badan

3. Body Surface Area (BSA)

4. Jenis Kelamin

5. Status Patologi

6. Toleransi Obat

7. Waktu Pemakaian

8. Terapi dengan obat yang diberikan bersamaan

9. Bentuk Sediaan & Cara Pemakaian

Dokter

Perawat Apoteker

Terapi

Pasien

Pencegahan Error

Pembungkusan

Serbuk, kapsul, cairan, setengah padat

Ukuran sendok

• Sendok teh/cth (5ml)

• Sendok makan/C (15ml)

• Sendok bubur/Cp (10ml)

Pengukuran obat-dosis tepat

Ukuran yang dipakai

− Padatan : gram, miligram

− Cairan : cc, mL, L (BJ)

− Tube, pulv, syrup, Fl (fles), gtt, ampul

− Angka romawi : X, L, M

Timbangan

• Timbangan kasar (menimbang > 1 kg)

• Timbangan besar (timbangan gram, > 1 g)

• Timbangan kecil (>50 mg)

• Timbangan halus/timbangan mg (< 50 mg)

Penimbangan

− Untuk setengah padat : perkamen dilapisi parafin

− Untuk zat-zat kental : perkamen/cawan penguap

− Cairan : gelas ukur (cc), botol/cawan penguap (g)

Pengukuran obat-dosis tepat

Dosing in Children

• There are seven distinct age

groups that are associated with

different drug Cl and hence

dosing requirements.

• Note that four of these ages are

related to the paediatric age

group. This reflects that the

child is a continually changing

pharmacokinetic and

pharmacodynamic environment.

The younger the child, the

greater the rate of change.

• Dosing in children under 6

months of age is very

complicated a specialist advice

is usually needed.

• Body Surface Area (BSA)

calculation may be used when

an establish dosage has not

been determined by the drug

company, as with some

anticancer or specialized

drugs.

Dosage: the determination and regulation of the

size, frequency, and number of doses

Perhitungan TM untuk Anak-anak

• Rumus Young

(anak ≤ 8 tahun)

tahun, orang dewasa : 20 tahun)

• Rumus Dilling

(anak > 8 tahun)

• Rumus Talbot

(Berdasarkan luas permukaan tubuh)

(Lpb orang dewasa = 1,73 m2)

• Rumus Fried

(bayi ≤ 1 tahun,n= dalam bulan)

• Rumus Clark

(berdasarkan berat badan dalam pon)

• Rumus Evans

anak-anak

n = umur yang akan datang

untuk obat antiinfeksi.antibakteri

n = umur anak sekarang

untuk obat sensitif (opiat)

n = umur yang sudah lewat

..cont

Patients: 6 months–12 years

• Use surface area (SA) approach (Talbot)

1. Using nomograms :

Read SA from a nomogram

..cont

2. Without

nomograms

SA(m2):

4W(kg) + 7

W (kg) + 90

…cont

3. Using a calculator:

• In the absence of an estimate of surface area,

an adjusted body weight can be used as

follows:

• This equation is derived from the fact that

weight to the power of 0.7 (wt0.7) relates

better to surface area than to weight alone.

Dosing in Pregnancy

Pregnancy

Drug effects

…cont 1. Avoid all drugs if possible, including social drugs (e.g.

smoking, alcohol, caffeine)

2. Avoid drugs in the first trimester

3. Choose drugs of proven safety or least toxicity

4. Use short courses and the smallest doses

Dosing in Geriatric

Pada umumnya kecepatan absorbsi obat lebih lambat

pada lansia dari pada dewasa muda karena faktor-faktor

berikut:

1. Berkurangnya sekresi getah lambung sehingga

kecepatan disolusi sediaan tablet & kapsul menurun,

juga kadar ionisasi obat

2. Perubahan mukosa G.I. Dapat memperlambat transpor

aktif obat

3. Perubahan kecepatan pengosongan lambung, motilitas

usus, menurunnya aliran darah ke mesenterik

Membuat Serbuk Percobaan

Cara:

Semua zat dicampur (1/3-½ dari seluruh

campuran dalam resep), kemudian ditimbang 3

sendok rata dari serbuk percobaan, sehingga bisa

diketahui berat rata-rata 1 sendok. Bila sudah

diketahui berat 1 sendok, dapat diketahui

dosisnya, apakah melebihi DM atau tidak.

Cont’

Contoh : R/ Natrii Subcarbonas 70

Papaverini HCl 2 sekali 250 mg (papaverine HCl)

Magnesii Carbonas 7 sehari 1 gram

Elaeosacch. Anisi 10

Kaolin 7

Mds. 3.dd.cth.1

Pro. Tn. Anwar

Caranya :

Seluruh serbuk ditimbang, kecuali papaverini HCl, lalu ditimbang 3 sendok teh

rata (misal 1 sendok teh rata = 4 gram).

Seluruh campuran beratnya = 96 gram

Seluruh campuran ada = 96/4 = 24 sendok teh

1 sendok teh mengandung Papaverini HCl = 1/24 x 2 g

= 83,30 mg

Dosis sekali = 83,30/250 -------------------kurang dari DM

Dosis sehari = 3 x 83,30 -------------------- kurang dari DM

1000

Dosis maksimum sekali dan sehari tidak dilampaui, maka campuran serbuk dapat

dibuat dan diserahkan kepada pasien.

Contoh kasus 1

•How many milligrams of a drug are in two tablets if one tablet contains 5

mg of the drug?

State the problem as a proportion:

5 mg : 1 tablet :: X : 2 tablets

Remember the product of the means equals the product of the extremes:

1 tablet × X = 5 mg × 2 tablets

Solve for X. Divide each side of the equation by the known value, 1 tablet,

and cancel units that appear in both the numerator and denominator:

Contoh kasus 2

•A patient is scheduled to receive 0.05 mg levothyroxine P.O., but the only

drug on hand is in tablets that contain 0.025 mg each. How many tablets

should you give?

State the problem as a proportion:

0.025 mg : 1 tablet :: 0.05 mg : X

The product of the means equals the product of the extremes:

1 tablet × 0.05 mg = 0.025 mg × X

Solve for X by dividing each side of the equation by 0.025 mg and canceling

units that appear in both the numerator and denominator. Carefully check

the decimal placement.

Contoh kasus 3 •Your patient is receiving 500 mg of cefaclor in an oral suspension. The label reads

250 mg/5 ml, and the bottle contains 100 ml. How many milliliters of the drug

should you give?

1. Set up the first fraction with the known solution strength:

2. Set up the second fraction with the desired dose and the unknown number of

milliliters:

3. Put these numbers into a proportion:

4. Cross-multiply the fractions:

5. Solve for X by dividing both sides of the equation by 250 mg and canceling units

that appear in both the numerator and denominator

You'll need to administer 10 ml of cefaclor to the patient.

Contoh kasus 4 A drug order calls for 60 mEq potassium chloride liquid as a one-time dose, but the

only solution on hand contains 20 mEq/15 ml. How many tablespoons should you give

the patient?

1. Convert the milliliters to tablespoons by using a conversion table. You'll see that

15 ml equals 1 tbs; therefore, 20 mEq of the solution on hand equals 1 tbs.

2. Set up the first fraction with the amount desired over the amount you have:

3. Set up the second fraction with the unknown amount desired—X—in the

appropriate position:

4. Put these fractions into a proportion:

5. Cross-multiply the fractions:

6. Solve for X by dividing each side of the equation by 20 mEq and canceling units

that appear in both the numerator and denominator: X = 3 tbs

Contoh kasus 5

Contoh kasus 6

Contoh :

R/ Atropini Sulfas 0,5 mg

Bellad. Extr. 15 mg

Lactose q.s

m.f.Pulv.dtd. No X

S.t.dd.P.I

Pro Tn. Abd. Hamid

Menurut FI ed. III (1979) :

DM untuk Atropini Sulfas :

Sekali = 1 mg

Sehari = 3 mg

Jadi :

Persentase satu kali =

Persentase satu hari =

Contoh kasus 7

Contoh :

R/ Atropini Sulfas 0,5 mg

Bellad. Extr. 15 mg

Lactose q.s

m.f. syr 60ml

S.t.i.d. I cth

Pro: Hamid (5 thn)

Menurut FI ed. III (1979) :

DM untuk Atropini Sulfas :

Sekali = 1 mg

Sehari = 3 mg

DM Rumus

5 x 1 = 0,29 mg

5+12

Persentase satu kali

60ml/5ml=12 sendok

1 x 0,5 = 0,041 mg

12

0,041 x 100 = 14,1%/sendok

0,29

Persentase satu hari

0,041 x 3 x 100 = 13,9%/sendok

0,88

Contoh kasus 8

If the maintenance dose of a drug for 70 kg adult

is 100 mg per day, what is the appropriate dose

for a 15 kg child? Using surface area

SA = 0.62 m2: Using weight

Pustaka

1. Antoon, Melody C., Collins, Marissa R.K., Frazer, Christine.,

Greenawalt, Julia A., et al. 2007. Dosage Calculations: An

Incredibly Easy! Pocket Guide. 1st Edition. Philadephia:

Lippincott Williams & Wilkins.

2. Begg, Evan J. 2003. Instant Clinical Pharmacology. Blackwell

Publishing Ltd UK.

3. Langley, Christopher A and Belcher, Dawn. 2008. Pharmaceutical

Compounding and Dispensing. Chicago: Pharmaceutical Press.

4. Pickar, Gloria D. 2007. Dosage Calculations: A Ratio-Proportion

Approach. 2nd edition. New York: Thomson.

OTT

Drug interaction:

Both in vitro and in vivo physically and chemically

interaction

Any in vivo incompatibility in which clinical effects of

one drug may be desirably or undesirably altered by

the prior, concurrent, or subsequent administration of

the same or additional exogenous substances.

Interaction

Foods

Chemical

Physyical

Pharmacology

OTT

Pustaka

Martin, Eric W. 1971. dispensing Of Medication: Formerly husa’s

Pharmaceutical Dispensing. 7th edition. Pennsylvania: Mack

Publishing. 113-175

Terima Kasih The only source of knowledge is experience

-Albert Einstein-